Notably, the device doesn't require a power supply, which tends to account for half the weight of similar implants and needs regular replacement.

"While we have gotten very good at shrinking electronic and mechanical components of implants, energy storage has lagged in the move to miniaturize," says professor Teresa Meng.

"This hinders us in where we can place implants within the body and also creates the risk of corrosion or broken wires, not to mention replacing aging batteries."

Poon's devices consist of a radio transmitter outside the body which sends signals to an independent device inside the body that picks up the signal with an antenna of coiled wire.

The transmitter and the antennae are magnetically coupled, so that any change in current flow in the transmitter induces a voltage in the other wire. The power's transferred wirelessly and can be used to run electronics on the device and propel it through the bloodstream.

The development rests upon Poon's discovery that radio waves travel much farther in human tissue than originally thought.

"When we extended things to higher frequencies using a simple model of tissue, we realized that the optimal frequency for wireless powering is actually around one gigahertz, about 100 times higher than previously thought," she says.

More significantly, however, this means that antennae inside the body can be 100 times smaller and still deliver the necessary power.

Poon's developed two types of self-propelled device. One drives electrical current directly through the fluid to create a directional force that pushes the device forward and can move at just over half-a-centimeter per second.

The second type switches current back-and-forth through a wire loop to produce a swishing motion similar to the motion a kayaker makes to paddle upstream.

"There is considerable room for improvement and much work remains before such devices are ready for medical applications," says Poon. "But for the first time in decades the possibility seems closer than ever."